I find that most places in the UK you can either use with a free TheCloud account, or roaming on Boingo. So, a one month Boingo subscription may well work for your needs

That said, given your requirements, I'd suggest you just get a UK PAYG (pay as you go) sim card, pop a few GBs of data on it, then either sling it in your smartphone or get a MiFi type thingy and put it in that